Portable small-sized electronic equipment, such as cellular phones, have been recently required to be multi-functional and to have further-reduced size, weight, and thickness. Functional components of such equipment are also required to have similar features.
A conventional push switch as the functional component will be described with reference to FIG. 10 to FIG. 12.
FIG. 10 is an exploded perspective view of the conventional push switch. FIG. 11 is a sectional view of the switch. FIG. 12 is a sectional view of the switch for showing a central fixed contact cut along a line 12—12 of FIG. 10. A box-like case 1 made of insulating resin has a recess being open upward, and includes a central fixed contact 2 and outer fixed contacts 3 and 3A at the inner bottom of the recess. The outer fixed contacts 3 and 3A are arranged symmetrically about the central fixed contact. The fixed contacts 2 and 3 are connected to a first terminal 4 and a second terminal 5 protruded outside the case 1, respectively.
The first terminal 4 having the central fixed contact 2 at its end and the second terminal 5 having the outer fixed contacts 3 and 3A at its end are formed by punching and bending a conductive metal sheet, and are secured in the case 1 by insert-molding. A middle portion 6 between the central fixed contact 2 and the first terminal 4, and a middle portion 7 between the outer fixed contacts 3, 3A and the second terminal 5 are embedded in the case 1 covering the middle portions completely.
An outer end portion 8A of a dome-shaped movable contact 8 formed of elastic metal sheet is placed on the outer fixed contacts 3 and 3A exposed and fixed at the inner bottom of the recess of the case 1. The movable contact 8 is positioned and accommodated in the recess of the case 1. An underside of a central portion 8B of the movable contact 8 is apart from and opposed to the central fixed contact 2 exposed at the inner bottom of the recess.
As shown in FIG. 12, the middle portion 6 extending from the central fixed contact 2 is bent downward at a position close to an outer end portion of the central fixed contact 2 and is embedded in the resin of the case 1. The middle portion 6 extends to a horizontal portion 6A covered with the resin of the case 1, and is led out as the first terminal 4.
The portion where the horizontal portion 6A corresponds to the position of the outer end portion 8A of the movable contact 8. However, since the horizontal portion 6A is embedded in the resin forming the bottom of the recess of the case 1 as described above, the movable contact 8 does not contact the middle portion 6 of the central fixed contact 2.
The opening of the case 1 is covered with flexible insulation sheet 9 disposed on the case 1.
An operation of a conventional push switch having the above configuration will be described.
When the central portion 8B of the dome-shaped movable contact 8 is pressed via the insulation sheet 9, the dome-shaped portion of the movable contact 8 is reversed with a click feel, and the underside of the central portion 8B then contacts the central fixed contact 2. At this moment, the outer fixed contacts 3 and 3A become conductive with the central fixed contact 2 via the movable contact 8, and the second terminal 5 and the first terminal 4 which are connected to the fixed contact 3, 3A and the fixed contact 2, respectively, become conductive with each other, thus causing the push switch to be turned on.
Upon an operation force being released, the movable contact 8 is restored to its original dome shape rising upward with its elastic restoring force. Then, the underside of the central portion 8B moves away from the fixed contact 2, and thereby, the first terminal 4 and the second terminal 5 are electrically separated, thus causing the switch to be turned off.
In the conventional push switch, the surfaces around the middle portion 6 between the central fixed contact 2 and the first terminal 4, and the surfaces of the middle portion 7 between the outer fixed contact 3, 3A and the second terminal 5 are completely covered with the insulating resin of the case 1. Therefore, as shown in FIG. 12, the resin above and under the middle portions 6 and 7 embedded in the portion underneath the recess of the case 1 has to be thick enough to avoid defective molding of the resin. Particularly in order to prevent the horizontal portion 6A at the middle portion 6 between the central fixed contact 2 and the first terminal 4 from contacting the movable contact 8, the resin necessarily cover the relevant area completely. However, the thickness of the case 1 between the inner bottom surface of the recess and the bottom of the case 1 cannot be reduced more than a limitation, thus preventing the thickness of the push switch including the case 1 from being reduced.